An automated method for azimuthal anisotropy analysis in marine seismic data

Abstract

Interest in azimuthal anisotropy analysis on marine seismic data has grown significantly in recent years. One of the reasons for this growing interest is that insights can be gained from these analyses on fracture detection and pressure prediction. Another reason is that a number of 3-D processing problems, such as footprint and loss of frequency content in stacking, that are caused by azimuthal anisotropy can be solved if the effects of azimuthal anisotropy are taken into account. It is, therefore, important to quantify the azimuthal properties of 3-D seismic data. In this paper, we present an automated and efficient method for estimating the azimuthal anisotropy parameters for large volumes of data. The method is automated because it is data driven and it does not involve any picking of velocity or semblance. It involves mainly two steps: first, flattening the CMP gathers that have been NMO corrected to generate time-variant timeshifts; second, fitting these timeshifts to the azimuthal anisotropic traveltime equation in a least squares sense to generate the velocity ellipticity and its direction. Using a recent survey that was acquired off Western Australia, we demonstrate that this method is able to obtain dense anisotropies and directions in large-scale areas in an automated way.